Die package resonance is a concern in the performance power delivery networks (PDNs) due to the low loss nature of PDNs. In the case of semiconductor power supplies, such resonance is a well-known issue for PDN designers. For example, in case of power supplies to processor cores, malware has been spread that can cause the power supply to oscillate. Die package resonance is due to increases in the PDN output impedance as the system operating frequency increases, which can cause the supplied voltage to drop below specification when a high current is demanded by the load. The increased output impedance is due to inductance that is inherent in the package's conductors, which connect the semiconductor to its host system, and from the capacitance of decoupling capacitors, referred to as “decaps,” which are often added to the system to reduce the output impedance. The decaps lower the output impedance of the power delivery network, essentially storing and delivering energy to the semiconductor circuitry to keep the voltage at the desired level. However, the decaps do not entirely solve the problem. The decaps interact with the inductance of the package, forming a parallel LC “tank” circuit along with capacitances inherent in the semiconductor device. This circuit resonates to cause die package resonance at a resonant frequency. PDN output impedance also peaks at the resonant frequency, causing voltage to swing excessively.
There are a few existing solutions to help mitigate die package resonance. One approach is to use high quality, controlled-ESR (equivalent series resistance) capacitors on the package and the host circuit board to suppress the resonance. This solution is very costly. Another solution is adding an on-die dampening resistor in series to on-die decaps, which requires careful physical layout implementation. Often, designers also lower the impedance peak by reducing the package inductance and increasing the on-die decap capacitance, both of which have significant cost impact on product designs.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.